1. Field of the Invention
The present invention relates to a drawing apparatus drawing a dotted line and its drawing method.
2. Description of the Related Art
A drawing apparatus such as a computer aided design (CAD) apparatus and a map display apparatus is equipped with a function of displaying a dotted line, et cetera.
A patent document 1 notes recognition of a dotted line pattern by numerical data of a painting and a gap pitches when drawing a dotted line by using a predetermined dotted line pattern and a calculation of these pitches by using a characteristic of similarity of a triangle, thereby drawing the dotted line more naturally.
A patent document 2 notes an equipment of means for calculating a beginning point of the second straight line or straight dotted line, and thereafter, thereby making it possible to draw an edge part of a bold dotted line or an edge part of each segment of a bold dotted line.
The conventionally practiced is to display various forms of dotted lines by using reference images thereof.
FIG. 1 is a diagram showing a reference texture of a dotted line. FIG. 1 shows a reference texture in which two pixels of white and black pixels continue alternately. The arrows on the bottom side of the reference texture indicate reference coordinates and the designation of reference coordinates S0, S1, et cetera, makes it possible to read pixel data in sequence.
FIG. 2 is a diagram (1) describing a conventional drawing method for drawing a dotted line by using the reference texture shown by FIG. 1.
In the conventional method for drawing a dotted line, drawing pixel data designated by the reference coordinate S2, followed by drawing pixel data designated by the reference coordinate S3 is faced with the problem of a dotted line patterns overlapping with each other in the part shown by the dotted circle in FIG. 2, resulting in deforming the pattern.
The accordingly considered has been to draw a crook line part by using the same pixel data by fixing the crook line part to the coordinate of the reference coordinate S2 for example when drawing the crook line part of a dotted line, as shown in a diagram (2) of FIG. 2 describing a conventional drawing method for drawing a dotted line. Unnatural overlap of a dotted line pattern has been prevented by fixing a reference coordinate as described above.
Incidentally, in the case of drawing a thick black and white dotted line diagonally and displaying it in a display apparatus, there has been a problem of a contour of the dotted line being displayed jaggedly as shown in FIG. 4A. In order to alleviate such uneasiness in terms of a display, what has been practiced is to make the jagged contour inconspicuous by filtering the dotted line by a half tone as shown in FIG. 4B.
However, a gradation display of a dotted line and a drawing of the same pixel data by fixing a reference coordinate as shown in FIG. 3 result in the entire crook line part being drawn by half tone pixel data as shown in FIG. 5 if the pixel data to be drawn is fixed by the reference coordinate of half tone pixel data. As a result, there has been a possible problem of the straight line part of the dotted line being displayed in black, while the crook line part thereof being displayed in a half tone, resulting in the color of the dotted line being not displayed uniformly, as shown in FIG. 5.
[Patent document 1] Japanese Registered Patent No. 3524380 (i.e., Laid-Open Japanese Patent Application Publication No. 11-316851)
[Patent document 2] Laid-Open Japanese Patent Application Publication No. 2003-76995